16 M. E. Beyrich on the Goniatites 



the contrary, is a little deeper : the last rises evidently to 

 form a lateral saddle. It does not ascend, as in ^. subnau- 

 tilinus, quite to the suture, and is not cut off in an abrupt 

 manner, but inflected considerably upon the side. (See M. 

 von Buch, fig. 3 and 9. pi. I.) This difference is because in 

 A, subnautilinus each saddle that unites the lateral lobe with 

 the flat ventral lobe, which exists in that ammonite, is com- 

 pressed beneath the suture, in consequence of the decided 

 envelopment of the interior whorls. 



4. Ammonites compressus. PI. I. fig. 6 a, b. 



Spirula compressa. Gold/. Dechen Geogn. p. 536. 



Gyroceratites gracilis, H. v. Meyer. Act. Nat. Cur. 1831. XV. II. 

 p. 59. 



Bronn. Leth. geogn. p. 102. pl. I. fig. 6. 



The dorsal lobe very small, infundibuliform, two or three 

 times as deep as broad. The lateral lobe is almost en- 

 tirely wanting, or at most only indicated by a very imperfect 

 curve on the transverse plates of the chambers. The increase 

 in height is 0*3, the increase in breadth 0'5. There are 15 

 chambers in a whorl; the number of whorls is from 4 to 5. 

 This ammonite has not any part enveloped ; the innermost 

 whorls are entirely free. 



It is not an unfrequent fossil in the clay slate of Wissen- 

 bach (Thonschiefer), nevertheless the specimens are seldom 

 well preserved : they oflen w ant the innermost whorl, and fre- 

 quently the exterior portion or that destitute of chambers. This 

 must have been the reason why Goldfuss called it a Spirula, 

 and H. von Meyer made it a distinct genus, under the name 

 Gyroceratites. The lobe distinctly exists, though certainly 

 small, and proves it to be really a Goniatite. The whorls are 

 by no means separated one from another, as in the Spirula, 

 but in contact with each other, although but slightly. The 

 greatest thickness is in the middle of the side, which gradually 

 diminishes, both towards the back and towards the suture, in 

 such a manner that the section of the mouth is an ellipsis. 

 One consequence of this is, that in the casts where the shell 

 is wanting there is really a little interval between the whorls ; 

 that space appears still larger if the particles of schist between 

 these whorls have not been taken off with sufficient care. 



